This invention relates to numerical control machine tools such as numerical control lathes, and more specifically to an improvement in numerical control machines.
The tool slide of a numerical control lathe, which is movable in the X-axis and Z-axis direction, involves sliding errors, namely, a parallelism error which occurs when the direction of movement of the tool slide on the Z-axis is not parallel to the center line of rotation of the main spindle, and a right-angle error which occurs when the direction of movement of the tool slide on the X-axis is not orthogonal to the center line of rotation of the main spindle.
The sliding errors of the tool slide may be attributed to mechanical errors which are caused in manufacturing or assembling the lathe, and include a straightness error which occurs when the movements of the tool slide on the X-axis and the Z-axis are not straight, in addition to the above-described parallelism error and right-angle error with respect to a reference line (such as the center line of the main spindle).
In FIG. 1(a), the parallelism error of the Z-axis and the right-angle error of the X-axis with respect to the center line CL of the main spindle SP are represented by angles .alpha. and .beta., respectively.
FIG. 1(b) shows axes X' and Z' which have straightness errors, i.e., wind, in comparison with the ideal axes X and Z which has zero straightness error.
Heretofore, where the sliding errors exceed the allowable values, no method of compensating the sliding errors was provided for a numerical control machine tool. Accordingly, in order to eliminate the error, the machine tool was, for example, disassembled and then is assembled again. If the extent of sliding errors was excessive, the essential parts of the machine tool were machined again, which was a very costly procedure.